1. Technical Field
The disclosed subject matter relates generally to implantable medical devices and more particularly to implantable medical devices that are adaptable to one or more physiological conditions in a patient in which the devices are implanted.
2. Background Information
Various diseases and disorders of the nervous system are associated with abnormal neural discharge patterns. One treatment regimen for such diseases and disorders includes drug therapy. Another treatment technique includes the implantation in the patient of an implantable medical device that comprises a pulse generator for electrically stimulating a target location of the patient's neural tissue. In one such available treatment for epilepsy, the vagus nerve is electrically stimulated by a neurostimulator device substantially as described in one or more of U.S. Pat. Nos. 4,702,254, 4,867,164, and 5,025,807, all of which are incorporated herein by reference.
Some implantable pulse generators used for electrical stimulation of neurological tissue operate according to a therapy algorithm programmed into the device by a health care provider such as a physician. One or more parameters of the therapy may thereafter be changed by reprogramming the neurostimulator after implantation by transcutaneous communication between an external programming device and the implanted neurostimulator. The ability to program (and later re-program) the implanted device permits a health care provider to customize the therapy provided by the implanted device to the patient's needs, and to update the therapy periodically should those needs change.
It is desirable, however, for an implantable medical device, such as a neurostimulator, to be able to automatically detect the onset of one or more physiological parameters, particularly where the parameter(s) indicate the actual or impending occurrence of an undesirable physiological event, such as an epileptic seizure, and then initiate a therapeutic response specifically tailored to the physiological parameters detected in the body of the individual patient to mitigate or prevent the physiological event without the necessity of intervention by a health care provider. Detection of such physiological events is, however, complicated by physiological differences among patients. Improvements in this area are desirable.